The present invention relates to an elevated bridge, particularly to a railway elevated bridge infrastructure and the design method thereof.
Moreover, the present invention relates to a seismic reinforcement process for reinforcing a reinforced concrete (RC) member in which shear failure precedes bending failure against earthquakes.
Furthermore, the present invention relates to a seismic frame structure requiring seismic properties and the design method thereof, particularly to a seismic frame structure and design method which are applied to the infrastructure of an elevated bridge for use in roads, railways, and the like.
A bridge on which railways, and transport vehicles such as cars run includes a bridge crossing rivers, straits, and the like in a narrow sense, and also includes a so-called elevated bridge continuously constructed in the streets. Such elevated bridge is continuously constructed on the road, the railway, or the space over the river from the viewpoint of efficient land utilization, and the road or the railway under the elevated bridge is three-dimensionally crossed, which also contributes to the relief of traffic jams.
Additionally, such elevated bridge infrastructure is usually constructed as a rigid frame structure of a reinforced concrete (RC) in many cases, but during design/construction, of course, the soundness of the elevated bridge itself during an earthquake, and also the safety of the running transport vehicle have to be sufficiently studied.
Under the circumstances, the present applicants have proposed an elevated bridge infrastructure in which a damper-brace is disposed in the rigid frame of the reinforced concrete, and it has been found that both the seismic property and the running safety can be enhanced according to the constitution.
However, no seismic design method has been established, and the development of a design technique which can efficiently and economically secure the seismic property and running safety has been desired.
Moreover, different from the bending failure, the shear failure of an RC member rapidly advances due to lack of ductility, and brings a fatal damage to the structure in many cases. Particularly, the shear failure of a pillar material caused by the action of a seismic load causes large damage to the structure in many cases, and for a short pillar which has a small shear span ratio and onto which a large axial force acts, and the like, the concrete of a pillar core part bursts into destruction by the compound action of a large axial direction stress and shear stress, and the pillar rapidly loses its load bearing capacity.
Therefore, in the structure design, the shear failure has to be avoided to the utmost, and for the current RC member in which the shear failure possibly precedes bending failure, seismic reinforcement is necessary, such as the winding of carbon fibers around a periphery and the winding of steel plates.
In this method, it is possible to enhance the shear load bearing capacity of an RC member and prevent the shear failure beforehand, but on the other hand, since the carbon fiber has to be wound over the entire member length, construction requires much time, and the method cannot necessarily be optimum as the seismic reinforcement process from an economical point of view.
Moreover, the infrastructure of the elevated bridge in which the damper-brace is disposed in the RC rigid frame is expected in the future because the seismic property can be enhanced as described above. However, when a steel frame eccentric brace is disposed in the RC rigid frame and a damper is interposed between the steel frame eccentric brace and the RC rigid frame, and when the damper has a small allowable deformation amount, such as a hysteresis shear damper, the damper is first ruptured in a big earthquake, and there has been a problem in that the ductility of the RC rigid frame cannot sufficiently be utilized.
Furthermore, when the damper is ruptured with a relatively small deformation, the load bearing capacity of the damper or the RC rigid frame has to be increased, but in this case, a foundation and a pile are naturally required to have a load bearing capacity increase, and consequently, the entire structure has a large section, which has caused a cost problem.
Accordingly, it is an object of the present invention to provide an elevated bridge infrastructure and the design method thereof in which the seismic property and running safety can more efficiently and economically be secured.
It is a further object of the present invention to provide a seismic reinforcement process of an RC frame in which shear failure can be prevented beforehand without requiring much construction time.
It is another object of the present invention to provide a seismic frame structure and the design method thereof which can enhance the seismic property without providing a damper or an RC rigid frame with a large section.
With the foregoing object in view, the present invention provides a method for designing an elevated bridge infrastructure that includes an RC rigid frame and a damper-brace disposed in a structural plane. The method comprises the steps of: setting a target ductility factor xcexcd and a target natural period Td for the infrastructure in an assumed earthquake motion; obtaining a yield seismic coefficient corresponding to the target ductility factor xcexcd and the target natural period Td from a yield seismic coefficient spectrum corresponding to the assumed earthquake motion to provide a design seismic coefficient Kh, and obtaining a target yield rigidity Kd corresponding to the target natural period Td; using the design seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd and obtaining a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd; distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace; and setting member sections of the RC rigid frame and the damper-brace so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity, and displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
The present invention also provides an elevated bridge infrastructure comprising an RC rigid frame and a damper-brace disposed in a structural plane, wherein member sections of the RC rigid frame and the damper-brace are set by setting a target ductility factor xcexcd and a target national period Td of the infrastructure in an assumed earthquake motion, obtaining is a yield seismic coefficient corresponding to the target ductility factor xcexcd and the target natural period Td from a yield seismic coefficient spectrum corresponding to the assumed earthquake motion to provide a design seismic coefficient Kh, obtaining a target yield rigidity Kd corresponding to the target natural period Td, using the seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd, obtaining a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd, and distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace, so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity and displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
The present invention further provides a method for designing an elevated bridge infrastructure that includes an RC rigid frame and a damper-brace disposed in a structural plane. The method comprises the steps of: setting a target ductility factor xcexcd and a target natural period Td for the infrastructure in an assumed earthquake motion; obtaining an elastic response spectrum seismic coefficient corresponding to the target natural period Td from an elastic response spectrum corresponding to the assumed earthquake motion; applying the elastic response spectrum seismic coefficient and the target ductility factor xcexcd to Newmark""s rule of constant potential energy to calculate a design seismic coefficient Kh and obtaining a target yield rigidity Kd corresponding to the target natural period Td; using the design seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd and obtaining a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd; distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace; and setting member sections of the RC rigid frame and the damper-brace so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity, and displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
The present invention further provides an elevated bridge infrastructure comprising an RC rigid frame and a damper-brace disposed in a structural plane, wherein member sections of the RC rigid frame and the damper-brace are set by setting a target ductility factor xcexcd and a target natural period Td of the infrastructure in an assumed earthquake motion, obtaining an elastic response spectrum seismic coefficient corresponding to the target natural period Td from an elastic response spectrum corresponding to the assumed earthquake motion, applying the elastic response spectrum seismic coefficient and the target ductility factor Td to Newmark""s rule of constant potential energy to calculate a design seismic coefficient Kh, obtaining a target yield rigidity Kd corresponding to the target natural period Td, using the design seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd, obtaining is a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd, and distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace, so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity and displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
The present invention further provides a method for designing an elevated bridge infrastructure that includes an RC rigid frame and a damper-brace disposed in a structure plane. The method comprises the steps of: setting a target ductility factor xcexcd and a target natural period Td for the infrastructure in an assumed earthquake motion; obtaining an elastic response spectrum seismic coefficient corresponding to the target natural period Td from an elastic response spectrum corresponding to the assumed earthquake motion; dividing the elastic response spectrum seismic coefficient by a response modification factor determined by a structure type to calculate a design seismic coefficient kh, and obtaining a target yield rigidity Kd corresponding to the target natural period Td; using the design seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd and obtaining a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd; distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace; and setting member sections of the RC rigid frame and the damper-brace so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity, and displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
The present invention further provides an elevated bridge infrastructure comprising an RC rigid frame and a damper-brace disposed in a structural plane, wherein member sections of the RC rigid frame and the damper-brace are set by setting a target ductility factor xcexcd and a target natural period Td of the infrastructure in an assumed earthquake motion, obtaining an elastic response spectrum seismic coefficient corresponding to the target natural period Td from an elastic response spectrum corresponding to the assumed earthquake motion, dividing the elastic response spectrum seismic coefficient by a response modification factor determined by a structure type to calculate a design seismic coefficient kh, obtaining a target yield rigidity Kd corresponding to the target natural period Td, using the design seismic coefficient Kh to obtain a design horizontal load bearing capacity Hd, obtaining a displacement corresponding to the design horizontal load bearing capacity Hd as a design yield displacement xcex4d from the target yield rigidity Kd, and distributing the design horizontal load bearing capacity Hd to a horizontal force Hf to be borne by the RC rigid frame and a horizontal force Hb to be borne by the damper-brace, so that the RC rigid frame and the damper-brace resist the horizontal forces Hf, Hb with an ultimate load bearing capacity and the displacements corresponding to the horizontal forces Hf, Hb equal a product of the design yield displacement xcex4d and the target ductility factor xcexcd.
Here, by performing the steps until setting the member sections of the RC rigid frame and the damper-brace as described above, the section design of the elevated bridge infrastructure is completed once, but subsequently the set member sections may be checked.
As the infrastructure of the elevated bridge, the infrastructure comprising the RC rigid frame and the damper-brace disposed in the structural plane is considered. However, the damper-brace mentioned herein means a structure including a brace disposed in the structural plane of the RC rigid frame and a hysteresis damper interposed between the brace and the RC rigid frame, in the brace or between braces, and brace shapes such as Y, X and K types and the hysteresis damper types such as shear and bending types, are arbitrary. Moreover, the constitution of the RC rigid frame is also arbitrary, and for example, the presence/absence of a foundation beam is not limiting.
Moreover, the present invention is mainly applied to a railway elevated bridge, but its use is arbitrary, and a highway elevated bridge is also included.
The present invention further provides a seismic reinforcement process of an RC frame comprising the steps of: partially cutting a main reinforcement bar of an RC member to shift failure property of the RC member from a shear failure preceding type to a bending failure preceding type.
The present invention further provides a seismic reinforcement process of an RC frame comprising the steps of: partially cutting a main reinforcement bar of an RC pillar member constituting an RC rigid frame to shift failure property of the RC member from a shear failure preceding type to a bending failure preceding type; and attaching a damper-brace mechanism in a plane of the RC rigid frame.
The present invention further provides a seismic frame structure comprising: an RC rigid frame including a pair of pillars vertically disposed in positions opposite to each other and a beam extended between tops of the pillars; an inverse V-shaped or V-shaped eccentric brace material disposed in a structural plane of the RC rigid frame and having both ends pin-connected to vicinities of middle positions of the pillars; and a damper interposed between an upper end of the inverse V-shaped eccentric brace material and the beam or between a lower end of the V-shaped eccentric brace material and a foundation beam for connecting leg parts of the pillars.
The present invention further provides a design method for a seismic frame structure that includes an RC rigid frame including a pair of pillars vertically disposed in positions opposite to each other and a beam extended between tops of the pillars, an inverse V-shaped eccentric brace material disposed in a structural plane of the RC rigid frame and having both ends pin-connected to vicinities of middle positions of the pillars, and a damper interposed between an upper end of the inverse V-shaped eccentric brace material and the beam. The method comprises the steps of:
modeling the seismic frame structure by disassembling the seismic frame structure into two models, i.e. an RC analysis model obtained by replacing a rigid joint of the RC rigid frame with a rotational spring and a damper-brace analysis model obtained by replacing the pillar and the beam with a virtual rigid pillar and a virtual rigid beam, pin-connecting the virtual rigid pillar to the virtual rigid beam, and interposing the damper between the virtual rigid beam and the upper end of the eccentric brace material;
in design of an external force P to be exerted to the seismic frame structure, obtaining a load Pdb of the damper-brace analysis model from the following equation,
Pdb=(hxe2x80x2/h)Hb
in which hxe2x80x2 denotes a height from a leg part of the virtual rigid pillar to the virtual rigid beam, hxe2x80x2 denotes a height from a brace connecting position of the virtual rigid pillar to the virtual rigid beam, and Hb denotes a damper load displacement characteristic, and obtaining a load Prc of the RC analysis model from the following equation,
Prc=Pxe2x88x92Pdb;
and
exerting Pdb to the damper-brace analysis model, exerting Prc to the RC analysis model to perform individual elasto-plastic analyses, and performing a section design of the seismic frame structure.
The site to which the seismic framework structure according the present invention is to be applied is arbitrary, and the present invention may be applied, for example, to a building seismic wall, or a bridge pier as the elevated bridge infrastructure. Additionally, the elevated bridge conceptually includes elevated bridges for railways, highways, and the like, and needless to say, its use is arbitrary.
A steel frame brace material can mainly be employed as the eccentric brace material.
For the damper, a hysteresis shear damper constituted from an excessively soft steel, a slitted thin steel plate, or the like is typically used, but a damper of any principle or structure may be used as long as a damping is generated by relative horizontal deformation and the sufficient deformation cannot be secured. A hysteresis bending damper, and the like can also be employed.
When both ends of the eccentric brace material are pinned to certain places of the pillars, xe2x80x9cthe vicinity of the middle positionxe2x80x9d of the present invention means an appropriate position between the pillar leg part and head part excluding these parts, and is not limited to a pillar bisector point, and the setting of (hxe2x80x2/h) is a matter of design.